They were issued under NAB's so-called Introducer Program, where the bank pays commissions to businesses such as financial planning and real estate agencies that refer customers who then take out a mortgage.

NAB said it uncovered the problems in October 2015 and told the Australian Securities and Investments Commission the following month.

"Since then, NAB has provided regular updates to ASIC on the progress of its investigation," Mr Haggar said.

Mr Haggar was brought into the chief customer role in August last year to clean up the mess, it is believed.

Twenty bankers in New South Wales and Victoria had their employment terminated or had left NAB, he said.